Friction Damper

ABSTRACT

The invention relates to a friction damper comprising at least two guided relatively displaceable assemblies ( 100, 200 ), one of which is connected to a fixed reference and the other is movable, an intermediate member ( 300 ) which rests on the first assembly ( 100 ) and is relatively frictionally movable with respect thereto by an applied force and elastic means ( 400 ) acting upon said intermediate member. Said invention is characterised in that said elastic means ( 400 ) at standstill loads said intermediate member ( 300 ) resting on the first assembly ( 100 ) and the device also comprises control means ( 500 ) disposed between the intermediate member ( 300 ) and the second assembly ( 200 ) in such a way that the relative displacement between the two assemblies ( 100, 200 ) in a first relative displacement direction therebetween is braked by a friction force defined by the elastic means ( 400 ), while in the second relative displacement direction between the two assemblies ( 100, 200 ), while the control means ( 500 ) acts on the elastic means ( 400 ) in order to modify the force applied on the intermediate member ( 300 ), in the second relative displacement direction between the two assemblies ( 100, 200 ).

The present invention relates to the field of friction dampers.

More precisely, an object of the present invention is to improve themeans described in document FR-A-2 697 881.

Said document describes a friction damper that uses:

friction as a physical energy-absorption phenomenon;

buckling as a controlled device for loading friction surfaces; and

a control device allowing loading of the device.

The device thus described in document FR-A-2 697 881 looks verypromising.

However, it requires a relative displacement between the frictionsurfaces in order to allow implementation of the friction. The responsecurve of a device of this type consequently exhibits two-stage loading.It is illustrated in FIG. 1.

That figure represents, as “Phase 1”, an initial loading phase, duringthe abovementioned relative displacement, and as “Phase 2” the nominalfunctioning phase of the damper.

A person skilled in the art will understand that Phase 1, whichcorresponds to the initial travel necessary before any nominalfunctioning, delays the functioning of the damper.

Furthermore, the embodiments presented in document FR-A-2 697 881 usewashers allowing buckling, which act between a shaft and a bore. Thesewashers are notched by radial slots that open out alternately on theirouter periphery and their inner periphery. They have a globally conicalgeometry when the damper is at rest. The initial geometry of this restposition conditions the proper functioning of the damper. It thusrequires a very refined embodiment, which generates significantmanufacturing costs.

An object of the present invention is to propose a novel concept offriction damper that enables these two problems to be overcome, i.e. onethat makes it possible to prevent a damper response that is delayed byan initial loading travel and, furthermore, one that makes it possibleto reduce the manufacturing cost as compared to the arrangementsdescribed in document FR-A-2 697 881.

This object is achieved within the context of the present invention byvirtue of a friction damper that comprises:

at least two guided relatively displaceable assemblies, one connected toa fixed reference, the other movable,

an intermediate member bearing against the one first of the assembliesand relatively frictionally displaceable with respect to this firstassembly through the effect of an applied force,

elastic means acting on the intermediate member, characterized in that

the elastic means, at rest, load said intermediate member bearing on thefirst assembly, and

in that the device also comprises control means arranged between theintermediate member and the second assembly such that in a firstdirection of relative displacement between the two assemblies therelative displacement between them is braked by a friction force definedby the elastic means, while in the second direction of relativedisplacement between the two assemblies the control means act on theelastic means in order to modify the force exerted on the intermediatemember.

According to another advantageous characteristic of the presentinvention, the elastic means bear between two separate zones of theintermediate member.

Further characteristics, objects and advantages of the present inventionwill become apparent on reading the following detailed description, andwith reference to the appended drawings, which are given by way ofnon-limiting examples, and in which:

FIG. 1 described above diagrammatically shows the response curve of afriction damper according to document FR-A-2 697 881;

FIG. 2 shows an exploded view of the principal component parts of adamper according to the present invention;

FIG. 3 shows a view of the same damper according to the presentinvention, in the assembled position;

FIGS. 4, 5 and 6 show three variant embodiments of elastic means thatcan be used within the context of the present invention;

FIG. 7 shows the functioning of the damper according to the presentinvention, in one displacement direction;

FIG. 8 shows the functioning of the same damper according to the presentinvention, in the opposite displacement direction; and

FIG. 9 shows the response curve obtained with a damper according to thepresent invention.

The appended FIGS. 2 and 3 show a friction damper according to thepresent invention.

These figures show two assemblies 100, 200 capable of relativedisplacement, an intermediate member 300, elastic means 400 and controlmeans 500.

One of the two assemblies 100, 200, which are capable of relativedisplacement and are guided, is connected to a fixed reference and theother is movable. Arbitrarily, with reference to the appended FIGS. 2and 3, the assembly 100 may be considered to be connected to the fixedreference and the assembly 200 to be movable relative to thefirst-mentioned assembly 100. However, this arrangement is not mandatoryand, as appropriate, it is possible to envisage the assembly 200 beingthat which is connected to the fixed reference and the assembly 100being the movable assembly.

Moreover, the concrete embodiment of the two assemblies 100, 200 may bethe subject of a very large number of variant embodiments. Thatillustrated in the appended figures should in no way be considered aslimiting.

According to the particular embodiment illustrated in the appendedfigures, the assembly 100 is formed from a tubular element 102, forexample an element that is symmetrical in revolution about an axis 104.More specifically still, according to the representation given in FIG.3, the tubular element 102 is closed off at one end by a partition 106.In a variant embodiment, however, this partition may be omitted.Furthermore, according to the representation given in FIG. 3, thetubular element 102 is provided, on its second axial end, with a secondtransverse partition 108 that has a central through-passage.

According to the representation given in FIGS. 2 and 3, the secondassembly is formed from a rectilinear rod 202 that passes through thepassage in the abovementioned partition 108 and is thus slidably guidedrelative to the assembly 102 along the axis 104.

The intermediate member 300 is designed in order to bear against theassembly 100. It is capable of relative displacement with regard to thelatter, with friction, through the effect of a force applied by theelastic means 400.

The intermediate member 300 may also be the subject of a number ofvariant embodiments.

According to the particular, non-limiting embodiment given in theappended FIGS. 2 and 3, this intermediate member 300 comprises a tubularsleeve 302 arranged on the inside of the tubular element 102. Thedimension of the outside cross section of the intermediate member 300globally complements the dimension of the inside cross section of thetubular element 102. It will be noted that the latter preferably has aconstant cross section over its entire length.

The tubular sleeve 302 is preferably provided, on one of these axialends (facing the abovementioned partition 106), with a partition 304transverse to the axis 104.

Preferably, the tubular sleeve 302 is produced from a material thatallows a radial extension through the effect of the loading of theelastic means 400 in order to press the intermediate member 300 againstthe inner periphery of the tubular element 102. In a variant embodiment,the tubular sleeve 302 joined to the partition 304 may be provided witha plurality of cutouts or axial slots, i.e. parallel to the axis 104allowing the abovementioned deformation, bearing against the innersurface of the tubular element 102 through the effect of the loading ofthe elastic means 400.

More precisely still, it will be noted, when examining the appendedFIGS. 2 and 3, that the tubular sleeve 302 is preferably provided on itsouter surface, over part of its length, with an extra thickness 306 thatforms a deformable zone bearing, by friction, between the inner surfaceof the tubular element 102.

Moreover, preferably, the intermediate member 300 is provided with meansthat make it possible to contain the elastic loading means 400, whichconstitute a device for loading by means of buckling.

Preferably, these means for confining the elastic means 400 are formedfrom an annular groove 308 provided on the inner periphery of thetubular sleeve 302.

Lastly, preferably, the intermediate member 300 is also provided withmeans 310 that make it possible to limit the relative displacementbetween the intermediate member 300 and the control means 500 associatedwith the assembly 200.

According to the particular, non-limiting embodiment shown in theappended FIGS. 2 and 3, these latter means are formed from an annularrib 310 projecting from the inner surface of the tubular sleeve 302 atits opening contour opposite the partition 304.

The control means 500 are arranged between the intermediate member 300and the second assembly 200. They are designed such that, in a firstdirection of relative displacement between the two assemblies 100 and200, the relative displacement between them is braked by a frictionforce defined by the elastic means 400, while in the second direction ofrelative displacement between the two assemblies 100 and 200 the controlmeans 500 act on the elastic means 400 in order to modify the forceexerted on the intermediate member 300.

More precisely still, preferably, the control means 500 are formed froma plate 502 transverse to the axis 104, integral with an axial end ofthe rod forming the second assembly 200. The plate 502 has an externaldiameter that is at least slightly smaller than the inside cross sectionof the tubular sleeve 302 but slightly larger than the internal diameterof the rib 310.

A person skilled in the art will understand that, thus, when the plate502 is engaged in the tubular sleeve 302, the plate 502 limits therelative displacement between the assembly 200 and the intermediatemember 300 when it abuts against the rib 310.

It will be noted that, according to the embodiment shown in FIGS. 2 and3, the control means 500 also comprise a finger 504 to the extensionextending beyond the plate 502, axially, along the axis 104, toward theelastic means 400. This finger 504 is capable of loading the means 400when the assembly 200 is displaced toward the right according to therepresentation of FIGS. 2 and 3 in order to modify the force exerted bythe elastic means 400 on the intermediate member 300, after cancellationof the play that exists initially.

The elastic means 400 allow loading of the contact surfaces 302/102.These elastic means 400 may be the subject of a number of variantembodiments. They may consist of a multitude of washers of variedshapes, as illustrated in FIGS. 4 to 6, in order to allow buckling ofshafts during assembly.

FIG. 4 shows an embodiment of elastic washers in the form of afour-branch cross.

FIG. 5 shows an embodiment of circular geometry elastic washers thatcomprise a plurality of radial slots opening out on the outer periphery.

FIG. 6 shows a variant embodiment of elastic washers formed fromglobally rectilinear strips punched on their lateral edges.

Of course, the elastic means 400 may also comply with the arrangementsdescribed in document FR-A-2697881. That is to say, use may be made ofwashers of circular geometry that are notched by radial slots that openout alternately on their outer periphery and their inner periphery.

Furthermore, as may be seen in FIGS. 2 and 3, the device according tothe present invention is preferably supplemented by a return spring 600that, at rest, loads the plate 502, bearing against the rib 310.According to the particular embodiment given in FIGS. 2 and 3, thisreturn spring 600 is a flat-coil spring interposed between the axiallyouter surface of the rib 310 and a rib 506 provided on the rod 202, onthat side of the plate 502 that is opposite the finger 504.

The functioning of the device thus formed can now be described withreference to FIGS. 7 and 8.

FIG. 7 gives a diagrammatic representation of the functioning of thedevice when the second assembly 200 is displaced toward the rightrelative to the first assembly 100.

Conversely, FIG. 8 gives a diagrammatic representation of the deviceswhen the second assembly 200 is displaced toward the left relative tothe first assembly 100.

A person skilled in the art will understand that, when the secondassembly 200 is displaced toward the right relative to the firstassembly 100, the play that initially exists between the finger 504 andthe elastic means 400 is cancelled out. The finger 504 consequentlyloads the elastic means 400, deforms, and converts buckling intoflexure, and thus significantly reduces the application of pressure ofthe surfaces 302/102. The flexure force is thus limited and thedisplacement of the assembly 200 facilitated.

Conversely, when, as illustrated in FIG. 8, the second assembly 200 isdrawn toward the left relative to the first assembly 100, the abutmentof the plate 502 on the rib 310 maintains the play that exists betweenthe finger 504 and the elastic means 400. The intermediate member 300 isthen loaded by the elastic means 400, which maintain the application ofpressure of the tubular sleeve 302 against the inner surface of thetubular element 102. The displacement of the second assembly 200 is thenaccompanied by a frictional braking force. When the assembly 200 is nolonger being displaced toward the left, according to FIG. 7, the spring600 returns the system to the initial position.

The resulting force curve is illustrated in FIG. 9.

A person skilled in the art will understand that, as compared to thecurve illustrated in FIG. 1 according to the prior art, the presentinvention makes it possible to dispense with any initial loading phasethat is likely to delay braking of displacement.

Of course, the present invention is not limited to the embodimentsdescribed above, but encompasses all variant embodiments in accordancewith its spirit.

In particular, it is possible to envisage any variant embodiment for thegeometry of the pieces defined above. As appropriate, it is alsopossible to envisage providing a system for the multiplication of forcesbetween the finger 504 and the elastic means 400, in order to reduce thereturn force.

The device according to the invention may give rise to numerousapplications, for example the damping of the recoil of a firearm.

1. A friction damper comprising at least two guided relativelydisplaceable assemblies (100, 200), one connected to a fixed reference,the other movable, an intermediate member (300) bearing against the onefirst (100) of the assemblies and relatively frictionally displaceablewith respect to this first assembly through the effect of an appliedforce, elastic means (400) acting on the intermediate member,characterized in that the elastic means (400), at rest, load saidintermediate member (300) bearing on the first assembly (100) and inthat the device also comprises control means (500) arranged between theintermediate member (300) and the second assembly (200) such that in afirst direction of relative displacement between the two assemblies(100, 200) the relative displacement between them is braked by afriction force defined by the elastic means (400), while in the seconddirection of relative displacement between the two assemblies (100, 200)the control means (500) act on the elastic means (400) in order tomodify the force exerted on the intermediate member (300).
 2. The deviceas claimed in claim 1, characterized in that the elastic means (400)bear against two separate zones of the intermediate member.
 3. Thedevice as claimed in claim 1, characterized in that the first assembly(100) comprises a tubular element (102) and the intermediate member(300) comprises a tubular sleeve (302) arranged inside the tubularelement (102).
 4. The device as claimed in claim 3, characterized inthat the tubular element (102) has a constant cross section over theentire length of its inner surface.
 5. The device as claimed in claim 1,characterized in that the intermediate member (300) is capable ofdeformation, for example of radial extension, through the effect of theloading of the elastic means (400).
 6. The device as claimed in claim 1,characterized in that the intermediate member (300) comprises a tubularsleeve (302) provided with cutouts or slots suitable for allowing itsexpansion.
 7. The device as claimed in claim 1, characterized in thatthe intermediate member (300) comprises a tubular sleeve (302) providedwith an extra thickness (306) located on its outer surface and restingagainst the inner surface of the first assembly (100).
 8. The device asclaimed in claim 1, characterized in that the intermediate member (300)comprises means capable of containing the elastic loading means (400).9. The device as claimed in claim 1, characterized in that theintermediate member (300) includes a groove (308) capable of confiningthe elastic loading means (400).
 10. The device as claimed in claim 1,characterized in that the intermediate member (300) comprises means(310) capable of limiting the relative displacement between theintermediate member (300) and the control means (500).
 11. The device asclaimed in claim 1, characterized in that the control means (500)comprise a finger (504) carried by a plate (502) integral with thesecond assembly (200).
 12. The device as claimed in claim 1,characterized in that the elastic means (400) comprise a multitude ofwashers.
 13. The device as claimed in claim 1, characterized in that theelastic means (400) comprise means working in buckling.
 14. The deviceas claimed in claim 1, characterized in that the elastic means (400)comprise cross-form elastic washers.
 15. The device as claimed in claim1, characterized in that the elastic means (400) comprise circularwashers that include radial slots.
 16. The device as claimed in claim 1,characterized in that the elastic means (400) comprise globallyrectilinear strips punched on their lateral edges.
 17. The device asclaimed in claim 1, characterized in that it comprises return means(600).
 18. The device as claimed in claim 17, characterized in that thereturn means (600) load an element (502) of the control means (500)against an element (310) of the intermediate member (300).
 19. Thedevice as claimed in claim 1, characterized in that it comprises aforce-multiplication system associated with the control means (500).